Food derived or in vivo human purine is metabolized into hypoxanthine and xanthine, which can be further catalyzed by xanthine oxidase (XO) into uric acid. Uric acid is the final metabolized product of purine in human. Abnormal purine metabolism leads to hyperuricemia, then urate crystals accumulation in joint, causing joint deformation and gout formation. Currently, local male above thirty years old has gout as high as 3.3%. People in their thirties have the highest tendency of getting gout. This phenomenon indicates that fast economic growth enables our citizen to take more animal protein and high calorie food, which generate more young obese population, and lead to high uric acid population increasing dramatically.
Symptoms of gout caused by high uric acid include muscle spasm, local swelling, inflammation, joint pain, muscle fatigue, sense of pressure and myocardial infarction. There are several commercially available medicines for treating gout, such as benzbromarone (URINORM), probenecid, allopurinol, bucolome, cinchophan, and colchicine, wherein allopurinol is a commonly used drug in clinic. Functions of these drugs are inhibiting uric acid formation, removing extra uric acid in vivo, working in kidney to help reduce uric acid, inhibiting xanthine oxidase activity which is responsible for metabolizing xanthine into uric acid, and accelerating in vivo uric acid secretion. However, these uric acid excretion promoting drugs have certain side effects, such as urolithiasis, GI disturbance, jaundice, kidney overloading, allergy and anemia. Therefore, despite lots of available drugs for gout treatment, there is still need for new drug or food additive to reduce uric acid content and to treat gout as well as gout related symptoms.
Xanthine oxidase not only metabolizes xanthine into uric acid in vivo, but also generates superoxide radical (O2.−) and peroxide (H2O2) in the reaction. The biochemical reactions are shown below:

Due to the instability of free radical, it is extremely easy to react with cells and tissues in vivo, and the reaction is summed as oxidation which may lead to cell malfunction. For example, if the oxidation occurs on the lipid of cell membrane, it can change cell membrane permeability, and cell necrosis is observed when nutrient and metabolite are unable to pass through cell. If cell membrane damage rate is faster than cell regeneration rate, tissue function will be affected significantly. If the oxidation attacks protein, it will lead to protein losing normal physiological function and cause diseases. For example, if oxidation occurs in subcutaneous collagen tissue, it may cause aging by losing skin elasticity and hydration. Besides, free radical will destroy DNA, causing DNA breakage or base mutation. Once DNA is broken, it may repair abnormally and lead to mutation during human repair process. Base pair attacked by free radicals will generate some by-products which may cause genetic error and possibility of carcinogenesis. If human suffers long term serial damages as described above, all kinds of chronic diseases, aging, and cancer may come along.
Acacia belongs to Leguminosae, is a commonly seen plant in low altitude and hills. Currently, the main function of Acacia is for traditional fuel wood and for structural wood. Besides, Acacia is one of the allelopathic species. The compounds of Acacia confusa leave possess bioactivity proven in sea shrimp lethal test. Some researches found that Acacia extracts contains flavonoid (Lai Yeap Foo, Phytochemistry, Vol. 26, No. 3, pp. 813-817 (1987); Elfranco Malan, Phytochemistry, Vol. 33, No. 3, pp. 733-734 (1993); Wu et al., Journal of Agricultural and Food Chemistry, Vol. 56, No. 5, pp. 1567-1573 (2008); Lee et al., Journal of Natural Products, Vol. 63, No. 5, pp. 710-712 (2000); Tung et al., Food Chemistry, Vol. 115, No. 3, pp. 1019-1024 (2009); Wu et al., Journal of Agricultural and Food Chemistry, Vol. 56, No. 2, pp. 328-332 (2008); Lee et al., Bot. stud, Vol. 47, pp. 37-43 (2006) and Wu et al., Journal of Agricultural and Food Chemistry, Vol. 53, No. 2, pp. 5917-5921 (2005)). However, xanthine oxidase inhibition compounds from Acacia bark, heartwood, even leaves have not been discovered to date.